The present invention relates to an apparatus for preventing or suppressing vibrations of an image due to hand shakes and, more particularly, to an image sensing apparatus such as a video camera or the like, which comprises an anti-vibration function.
Recent video cameras normally have an anti-shake function. The anti-shake function includes optical correction and electronic correction.
In optical shake correction, a prism or lens member that can displace the optical axis of image sensing light is inserted into the optical path of the image sensing light that becomes incident on an image sensing element, and the optical axis is deflected in correspondence with shake, thus canceling a motion of an image arising from shake. As a shake detection means, it is a common practice to directly detect vibration components acting on a camera using an angular velocity sensor such as a vibration gyro and to integrate the outputs from the sensor so as to detect angular displacement of the camera.
On the other hand, the electronic shake correction function is often used together with motion vector detection that calculates the moving amount of a camera on the basis of a change in video signal between adjacent fields. When a partial video signal is extracted and read out from an image stored in a field memory for motion vector detection, the video signal is extracted to remove the detected motion of the image. As another electronic shake correction, an angular velocity sensor is used in vibration detection, and a partial image is extracted from an image output from the image sensing element to cancel a motion of that image and to output the extracted image.
Electronic shake correction is done at field periods since it is implemented by an electronic process for a video signal. Hence, the electronic shake correction cannot remove shake during exposure, but can attain a size and weight reductions compared to optical correction. Also, when a high-density, large image sensing element is used, the resolution of an image extracted from the sensed image signal can be increased, and deterioration of image quality which is inferior to the optical correction can be improved to some extent.
With a video camera, the user often senses an image while making a camera work such as panning, tilting, or the like, i.e., while he or she is intentionally moving the camera. Upon image sensing with such camera work, if the shake correction function is enabled, the limit of the correction range is reached soon to disturb the sensed image, and a response in a direction desired by the photographer is delayed. As a means for preventing such problems, an arrangement that suppresses correction capability by limiting shake correction is proposed (e.g., Japanese Patent Laid-Open No. 5-142614). Also, an invention that realizes natural panning even when the focal length enters an ultra telescopic range is proposed (Japanese Patent Laid-Open No. 9-51466).
In conventional panning control, when the level of a shake detection signal (or its processed signal) has exceeded a predetermined threshold value, the vibration correction capability is suppressed. Hence, in continuous video sensing, i.e., motion image sensing, the panning control makes the motion of an image on the frame during a transition to a panning mode unnatural.
In order to avoid such problems, an invention that changes the vibration correction characteristics to smoothly change the vibration correction capability along with an elapse of time is also proposed (Japanese Patent Laid-Open No. 8-313950).
However, where the proposed technique is applied to an optical or electronic anti-vibration device in which a vibration correction means is placed behind a zoom lens, it requires setting parameters for panning operation for each change in focal length, hence such device cannot be realized in practice.
Further, the proposed technique has not given a full consideration to various image sensing conditions in how applying restraints to the anti-vibration correction.
It is an object of the present invention to provide an image vibration prevention apparatus or image sensing apparatus that, in response to a panning operation, can easily and appropriately limit an correcting operation of the apparatus.
The above object is achieved by providing an image vibration prevention apparatus or image sensing apparatus comprising:
a vibration correction device for correcting a vibration of an image; and
a limiting device for calculating a ratio of an amount of vibration correction to be effected by said vibration correction device in accordance with an image shake condition, to a maximum value of vibration correction by said vibration correction device, and limiting an operation of said vibration correction device in correspondence with a calculation result.
The above object is also achieved by an image vibration prevention apparatus or image sensing apparatus comprising:
a vibration correction device for correcting a vibration of an image; and
a limiting device for, in response to a panning operation, limiting a correction operation of said vibration correction device, by applying different limitations in pitch and yaw directions to said vibration correction device.
Other features and advantages of the present invention will be apparent from the following description taken in conjunction with the accompanying drawings, in which like reference characters designate the same or similar parts throughout the figures thereof.